When negotiating a curve with a typical automotive-type vehicle, the resulting centrifugal forces roll the vehicle body and associated chassis (hereinafter jointly referred to as "body") about its roll center relative to the underlying suspension system, and also displace the body and suspension system laterally outwardly tending to cause the vehicle to pivot about its outer wheels. This latter tendency is commonly known in the motor vehicle art as the "jacking effect". During braking and acceleration, the resulting longitudinal forces acting on a typical automotive-type vehicle tend to pitch the body about its pitch center relative to the underlying suspension system and also tend to displace the body and suspension system forwardly during braking and rearwardly during acceleration to cause the vehicle to pivot about its front or rear wheels, respectively.
The locations of the roll center and pitch center are functions of the construction of the vehicle body and the configuration of the vehicle suspension system. In a conventional vehicle, the center of gravity of the vehicle is located above the roll center and pitch center. Since the centrifugal forces caused by cornering and the longitudinal forces caused by accelerating and braking act through the center of gravity of the vehicle, the magnitude of the couple tending to cause the body to roll about its roll center is a function of the magnitude of the centrifugal force and the vertical distance separating the center of gravity from the roll center and the magnitude of the couple tending to cause the body to pitch about its pitch center is a function of the magnitude of the longitudinal force and the vertical distance separating the center of gravity from the pitch center. These vertical distances are commonly known as the "roll couple" and "pitch couple", respectively.
In a typical vehicle, as the body rolls outwardly about its roll center, it tends to compress the outer suspension springs (relative to the radial center of the curve about which the vehicle is traveling) thus increasing the weight on the outer wheels while simultaneously unloading the inward suspension springs thereby reducing the weight on the inside wheels. As a result, the cornering traction of the vehicle is reduced. Also, as the body pitches forwardly about its pitch center during braking, it tends to compress the forward springs thus increasing the weight on the forward wheels while simultaneously unloading the rearward springs thereby reducing the weight on the rearward wheels. This resulting imbalance in the weight being carried by the forward and rearward wheels decreases the maximum braking capacity of the vehicle. The foregoing loading changes on the vehicle wheels caused by cornering and braking will occur simultaneously when the vehicle's brakes are applied while cornering, thereby potentially causing even greater imbalance of the weights on the vehicle wheels than caused by cornering alone or braking alone. This imbalance may result in the loss of substantially all of the traction of one or more wheels.
The lateral force tending to cause a vehicle to pivot about its outer wheels, i.e., jacking effect, acts through the portion of the vehicle known as the roll reaction center. The longitudinal forces tending to cause a vehicle to pitch about its forward or rearward wheels acts through the pitch reaction center. In a conventional vehicle, the roll reaction center coincides with the roll center and the pitch reaction center coincides with the pitch center. As a result, the magnitude of the jacking effect is a function of the magnitude of the centrifugal force and the elevation of the roll reaction center above the ground, and the magnitude of the pitching effect is a function of the magnitude of the longitudinal braking/acceleration force and the elevation of the pitch reaction center above the ground. With respect to the effect of cornering forces on a vehicle, the height of the roll reaction center above the ground is commonly known as the jacking couple, and with respect to the effect of braking and acceleration forces on the vehicle, the height of the pitch reaction center above the ground is commonly known as the pitching couple.
In conventional vehicles, attempts have been made to design the suspension system to minimize the height of the roll reaction center, thereby to reduce the jacking effect. Placement of the roll reaction center at a low elevation, however, results in the center of gravity of the body being located at a substantial distance above the roll center, thereby increasing the magnitude of the roll couple. The increase in the roll couple results in decreased stability of the vehicle, especially since in typical suspension systems the body roll and jacking effect are cumulative, both reducing the cornering ability of the vehicle.